Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first image in a sequence for a display screen or portion thereof with a graphical user interface showing the new design; and,

FIG. 2 is a front view of a second image thereof.

The outermost broken line rectangle shows the display screen or portion thereof and form no part of the claimed design. All other broken lines show portions of the animated graphical user interface and form no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-2. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM I claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 